The present invention relates to an apparatus for inspecting a defect from an image of an inspection object obtained by using an ultrasonic wave, an x-ray, or the like, and specifically to an inspection method suitable for an inspection of an inspection body having a multi-layer structure and a non-destructive inspection apparatus using the same.
As a non-destructive inspection method for inspecting a defect from an image of an inspection object, there are a method of using an ultrasonic image generated by irradiating the inspection object with an ultrasonic wave and detecting a reflected wave therefrom, and a method of using an x-ray image obtained by irradiating the inspection object with an x-ray and detecting an x-ray transmitted therethrough.
In order to detect a defect present in an inspection object having a multi-layer structure using an ultrasonic wave, a reflection property due to difference in acoustic impedance is generally used. The ultrasonic wave propagates through a liquid or solid material and generates a reflected wave at an interface between materials having different acoustic impedances or at a cavity. Since a reflected wave from a defect is different from a reflected wave from a defect-free portion in its strength, it is possible to obtain an image that exposes the defect present in the inspection object by visualizing reflection intensities at inter-layer interfaces of the inspection object.
Determination of presence of a defect in the obtained image of the reflection intensity is often performed visually by an inspector, which may lead to variation in the evaluation result due to the experience of each inspector. Moreover, major inspection objects such as semiconductors and electronic devices are increasingly miniaturized, making it more difficult to visually distinguish a defect from a normal pattern. Furthermore, multi-layer structures have become more popular to be adapted to multi-functionalization and miniaturization of mounting products, a WLP (Wafer Level package) method of handling the product in a form of a wafer until the final process of packaging is becoming a mainstream in the manufacturing scene. Thus, it is required for the ultrasonic inspection to detect a micron-order internal defect at a high speed with high sensitivity by separating the micron-order internal defect from a complicated pattern in the form of the wafer. However, this corresponds to detecting only a few pixels showing the defect from several tens of millions of pixels constituting an internal image, which is nearly impossible to be determined visually.
One conventional technique of automatically detecting a defect from an ultrasonic inspection image is a method described in Japanese Patent Laid-open No. 2007-101320 (Patent Document 1). This includes a function of sequentially generating and displaying ultrasonic inspection images, thereby extracting a candidate defect based on contiguity of a luminance distribution in each image. A defect and a noise can be distinguished by the length of the continuous repetition of the candidate defect. Furthermore, there is another method described in Japanese Patent Laid-open No. 2012-253193 (Patent Document 2). In this method, a presence of a void in a TSV (Through Silicon Via) in a three-dimensional integration structure is estimated based on ultrasonic scanning.